I’ve got a 150w panel fitted to the roof of the van but at this time of year it doesnt produce enough power to charge the battery. From the panel leads i’m getting about 10.5-11 volts which is less than the battery voltage. Its just got a basic PWM charge controller.

Would an MPPT controller produce more power, or are they not able to step voltage up if its only getting 10.5 from the panel?

If i fit another panel in series would this help, then the voltage would increase? If i do this do i have to get exactly the same panel, or can i use a different make, and can i use a different power output (eg 175W or does it have to be another 150W), i know if i increase the total panel power i’ll have to probably upgrade the charge controller

thanks

I’m no Solar expert but my MPPT has to see battery voltage +5v before it will start charging, so no I don’t think changing your controller will help with that.

2 panels in series should help though I think as long as your controller (or a new one) can take the voltage, which will be a lot higher in bright sun obviously.

Beware though you still might not get enough power for what you want without covering the roof in panels. In Scotland in winter I regularly only see 10% of my panels 270W output.

I’m in the Alps now in bright sun every day and the most I’ve seen is 125W so not even half of the panel max, due to the low sun.

First thing to check is your panel is actually outputting correctly.

Next I would check the controller.

The numbers your getting don’t sound right at all

I’ve got little experience other than the panels I fitted to out motorhome. First thing to remember is that at this time of year, low sun, cloud etc all massively blunt solar performance to the point that the output especially from horizontal panels could be close to zero. The voltage you were measuring? Was this open circuit from the panel or across the charge controller inputs/outputs? Definitely too low for any charging to take place. Open circuit voltage is well in excess of 12v. ISTR mine were about 17v perpendicular to strong sunlight.

I measured the voltage from the controller input terminals, where the panel wires go in, should i disconnect the panel and check?

an MPPT controller ‘should’ be able to take more advantage of winter sun to put in charger thana standard PWM.

However that relies on the panel outputting some charge in the first place. 10-11V sounds too low and will never get across. however I’ve just read above that is with it connected rather than an open circuit voltage.

Carefully, disconnect and check the voltage with no load connected. if you’re getting >12V then the panel should be ok, but is not outputting enough current to be useful. This coudl be down to a) panel knackered, b) controller not able to accept such small currents (mPPT may help) or c) its winter and there’s not much sun about

I’d wait until the sun is at its peak today, disconnect the panel & check the open circuit voltage. Is the panel going to be exposed fully? IE no overhanging trees.

Ok, as said previously wait until you have got reasonable light levels, disconnect the panel and check the open circuit voltage. If it is still at 10-11v then I would suspect there is a fault on the panel. From recent experience the panels rarely fail, but the circuit connections from the panel to the wiring can be very dodgy. If you get water ingress in to the connection on the panel you will have corrosion and potential shorting/leakage and a decrease in voltage. Depending how old the panel is it may be under warranty, but if not you can still repair it.
I have spent a lot of this winter repairing and replacing panels on our sites for this reason. A couple of photos would be useful especially of the panels.

thanks for the replies, will check again when its sunny.

Is it realistic for a 150w panel to charge a battery on winter days? And if not, would a second panel help (in series to boost the voltage up) or would the current still be so low that it would take forever to put any significant charge in?

Is it realistic for a 150w panel to charge a battery on winter days? And if not, would a second panel help (in series to boost the voltage up) or would the current still be so low that it would take forever to put any significant charge in

Depends where you are but ime yes..

I’m in Aberdeen Scotland and had 150w on my roof with one battery and it was fine – then doubled my batteries so doubled my panels.

Even in winter so long as I’m not sitting with an inverter plugged it keeps my battery up to spec.

Do have an mppt controller though

It depends on the size of battery that you want to charge. It also depends on your battery usage. I take it that it means you want to keep it topped up ready for occasional use, but let me know what the usage is. The bottom line is that assuming you are using a 110Ah leisure battery and want to keep it topped up then even a sub optimal 150W panel will keep it topped up.

Just for example I am charging 220 Ah batteries 240W array under trees with no direct sunlight on a flat roof. That is not ideal, but on another site I kept 3 x 55Ah batteries charged on 150W panel with continuous use (admittedly low 10s Watts use but 24/7). The site was ideal, but I would have problems in late Dec to Jan if the weather was overcast and raining during that time and no recharge occurred. I had to double to panels and split the power use to get it through that time for our use.

The panel should produce something close to it’s rated *voltage* when disconnected from the controller, even under poor lighting. If it isn’t, there’s a problem with the panel or the wiring to it.

If it’s a domestic panel, the open circuit voltage is probably about 20V.

My 160W panels were generating about 4AH useful power a day over Christmas. (See also here)